In conventional air-conditioners, wherein air in a room is conditioned by circulating it in the room via a heat exchanger, a cross-flow fan has been used, wherein the air being circulated flows across the fan.
The structure of a room unit for such an air-conditioner equipped with a cross-flow fan is shown in FIG. 6. FIG. 6 is used here, because its overall structure is substantially the same as that of the prior-art device, although it refers to an embodiment of this invention. It is a cross section of the room unit, wherein inlets 1a and 7a are provided in upper and front covers of a case 1 of the body of the unit, respectively, and wherein an outlet 1b is provided in a bottom portion of the body case 1. An air filter 6, a heat exchanger 2, and a cross-flow fan 3 are disposed sequentially in that order in a flow path 5 connecting the inlet 1a and the outlet 1b.
FIG. 7 is a perspective of the cross-flow fan 3. As shown in it, a plurality of supporting disks 3b are disposed on a shaft 3c at given intervals therebetween, and also a plurality of vanes 3a extend between the supporting disks 3b.
Such a cross-flow fan 3 is driven by an electric motor (not shown). The cross-flow fan 3 is disposed such that it is sandwiched between a rear-guider 1c and a stabilizer 4 so as to enhance the efficiency of the blowing air.
A tongue-shaped surface 4a is formed at the end of the stabilizer 4.
With the thus-structured unit, when the cross-flow fan 3 starts rotating, the warmed air through the heat exchanger 2 is blown from the outlet 1b into the room.
At that time a portion of the air blown from the cross-flow fan 3 impinges on the tongue surface 4a to be reabsorbed into the cross-flow fan 3, so that large concentric eddies, each of whose axis of rotation is eccentric to that of the cross-flow fan 3, are formed at the outlet part of the cross-flow fan 3.
These eddies are cut by each vane 3a to cause variations of pressure, thereby noises are generated.
These noises consist of first-order rotary sounds associated with intervals between adjacent vanes. The frequencies of the first-order rotary sounds are defined by N.times.Z, where N is the number of rotations per second and Z is the number of vanes 3a.
Conventionally it has been proposed that adjacent vanes 3a be disposed along the peripheries of the disks, with their intervals therebetween being disposed at random, to reduce the noises of the first-order rotary sounds.
However, it was found that, with vanes 3a being disposed at random intervals therebetween, when vanes having low absorbing ability (adjacent vanes disposed at short intervals) exist at both the inlet and outlet sides, the flow of the air from the fan was reduced, and that conversely, when vanes with high absorbing ability exist at both the inlet and outlet sides, the reverse phenomenon was brought about.
Thus, there was a problem in that, depending on the variations of the flow of air, the levels of vibrations and noises increased.
Therefore, the optimum intervals between the vanes 3a were determined through an experiment or the like.
However, optimizing the spacing or distribution of intervals of the vanes 3a was so difficult that there was a problem in that even if the above-mentioned first-order sounds were successfully reduced, those low frequency (1N-20N) rotary noises, which accompany by the rotations of the vanes 3a, were not successfully reduced.
Further, the concerned, parties including the applicant hereof, experimentally certified that a problem was observed when the noise level increased and there existed discontinuous variations thereof in a frequency area at around 8N, and listeners perceived an unpleasant hearing impression.
In view of such problems, this invention was made. The purpose of this invention is to provide a cross-flow fan and an air-conditioner for using it, wherein to realize a cross-flow fan with a low noise level the intensity and variations of the noise level at around 8N on the low-frequency side, as well as the noise level caused by first-order rotary sounds, are reduced, without any unpleasant impression being given to listeners.